1. Technical Field
The present invention relates to methods and apparatus for use in mixing and dispensing multi-component compositions such as dental cements or impression materials. More particularly, the present invention is directed to syringe mixing and dispensing methods and apparatus.
2. Background Information
Many modern formulations are packaged in two parts, often known as A and B components. Upon mixing, these A and B components typically undergo a chemical reaction which causes the resultant composition to "set up" in some desired manner.
In the dental field, for example, several two-part formulations currently enjoy wide use. Glass ionomer cements and resinous luting cements are frequently used for applications such as securing dental caps in place. Dental impressions are made using A and B components.
In order to work properly, it is important that the A and B components of these two component systems be mixed together rapidly and thoroughly and in the right proportions. Failure to mix rapidly can result in loss of valuable working time with the resultant composition, and can impact the ability to obtain a thorough mix as the composition begins to set up unevenly. Failure to mix thoroughly can result in a composition having less than optimum characteristics. For example, if a poorly mixed composition is used as a cement, it is possible that portions of the cement will fail to reach the chemical strength required for a long-term bond.
Problems of obtaining rapid and uniform mixing are often complicated by differences in the A and B components. Sometimes it is necessary to mix two liquids, while other times it is necessary to mix a powder with a liquid. Sometimes there are equal amounts of the A and B components, but other times there is more of one component than another. Sometimes the two components have similar viscosities, while at other times the two components have widely differing viscosities.
The primary means employed for mixing A and B components has been simple mechanical mixing, such as by means of a mixing bowl or pad and a stir instrument such as a spatula. This method tends to be somewhat messy and time consuming. It is difficult at times to gauge whether the mixing has been sufficiently thorough.
It is also difficult in some instances to prevent formation of small air bubbles in the mixed composition. During the mixing process itself, the stirring action of the spatula, or similar mixing instrument, introduces and causes air bubbles to be entrapped within the mixed composition. Further, most dental compositions are ultimately dispensed from a syringe in order to control the amount dispensed, to permit precise placement of the dental composition, and to prevent premature evaporation of constituents of the composition. This generally requires placement of the mixed compositions into a syringe. Additional air can become entrained during this step. Entrained air bubbles are usually detrimental.
Further, the simple process of mixing the components on a pad or in a bowl and then transferring them to a syringe takes time; this can lessen the available working time to actually utilize the composition. It is not uncommon for so much time to pass during the mixing and syringe-loading steps that the mixed composition becomes effectively unusable.
In an effort to overcome the time delays and the mess inherent in the approach set forth above involving mixing on a pad or in a bowl followed by loading into a syringe, attempts have been made to mix materials directly from a syringe or from a caulking gun. These attempts have involved the use of specially formed tips which effect some mixing as material is dispensed from the syringe or caulking gun. Although useful from the standpoint of minimizing the amount of time used to effect the mixing of A and B components, incomplete mixing is common. Furthermore, the mixing tips utilized are frequently expensive, and are difficult to reuse.